Drugs linked to 19 deaths are like having a “serial killer” on the loose, a coroner has warned.

John Leckey made the comment at one of a number of inquests into fatalities in Northern Ireland.

Meanwhile Coroner Suzanne Anderson, at a drug inquest into the death of Brian Mills, said on Thursday: “Hopefully action can be taken to stem the supply of these dangerous drugs.”

Mr Mills died after taking a tablet called a speckled cross.

A pathologist told the hearing on Thursday that the 19 deaths occurred between June last year and February and in each case the substance 4,4-Dimethylaminorex was present in the deceased’s bloodstream.

It was also warned that the substance could be in a number of different ecstasy-style pills.

After Thursday's inquest a senior police officer issued a statement to say that an extensive investigation is ongoing into a number of deaths linked to the substance.

Detective Superintendent Andrea McMullan warned that 4,4-Dimethylaminorex is “not confined to one particular brand of tablet” and “has been identified in a number of tablets and in a number of deaths”.

The inquest heard that hundreds more tablets, white with cherry imprints, were found at Mr Mills' house in Kircubbin, Co Down.

Mr Mills, 41, complained to his son James that he was too warm following an all-night drinking session at his home in August last year.

Minutes later he stopped breathing, appearing to be having a fit, James Mills told the inquest. Paramedics were unable to save him.

Ms Anderson added: “I think this case highlights very clearly the grave risks involved in taking illegal drugs and I think following all these deaths, this cluster of deaths, I certainly am pleased to know that the police are taking the matter seriously and are liaising with Forensic Science Northern Ireland (FSNI) and with the pathologist’s department.”

Dr Bernadette Prentice, a scientist from FSNI, analysed the victim’s blood for toxins and found 4,4-Dimethylaminorex, known as speckled cherries or speckled crosses.

A total of 287 tablets containing the drug were discovered at Mr Mills’ home by his brother, Leonard Mills. They were confiscated by police.

Dr James Lyness, assistant state pathologist in Northern Ireland, said Mr Mills’ death was one of several involving the drug.

He told the inquest: “There are 19 cases from 18 June 2013 to 6 February 2014 where the 4,4-Dimethylaminorex... is mentioned within the cause of death.”

Dr Prentice said the drug was not controlled (banned by legislation) in the UK.

She added: “4,4-Dimethylaminorex can be regarded as a novel psychoactive substance.

“It has rarely been encountered as a drug of abuse and consequently (there is) very little data.”

She said it could be sold as powder or tablets and was first found in the Netherlands in 2012 and later in Finland, Hungary - where there have also been deaths reported - and Denmark.

Police made several seizures of the substance in Northern Ireland last year and the PSNI’s organised crime anti-drugs unit is investigating, Dr Prentice told the inquest.

She said police had been holding meetings with forensic scientists and the pathologist’s department.

The toxicologist said a certified reference standard for testing was not available but there was little reason to doubt the accuracy of the results.

“It is clear that they will have some similarities to related stimulant drugs.”